Apparatus and method for slicing an ingot

ABSTRACT

A method for slicing an ingot may improve nanotopography at a surface of a wafer. In the method, an ingot is sliced into a plurality of wafers via a slurry while slurry is supplied to a moving wire. A first wire to form a first slicing portion at the wafer firstly slices one side of the ingot. A second wire secondly slices the remaining portion of the ingot to form a second slicing portion continued from the first slicing portion, wherein the first wire has a smaller diameter than that of the second wire.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication 10-2004-0096218 filed in the Korean Intellectual PropertyOffice on Nov. 23, 2004, the disclosure of which is incorporated hereinby reference.

BACKGROUND

1. (a) Technical Field

This application relates to an apparatus and a method for slicing aningot. More particularly, the present invention relates to an apparatusand a method for slicing an ingot capable of improving fine unevennessof a wafer, i.e., its nanotopography.

2. (b) Description of the Related Art

Generally, a wafer manufacturing process includes an ingot growingprocess, a slicing process, an edge grinding process, a lapping process,an etching process, a back side polishing process, a pre-anneal cleaningprocess, an edge polishing process, and a front polishing process. Inthe ingot growing process, silicon (Si) is induced from sand and is thenpurified to make a silicon raw material. A desired impurity is theninjected to make an N-type or P-type silicon ingot. In the slicingprocess, the N-type or P-type silicon ingot produced in the ingotprocess is cut to have a desired thickness. In the edge grindingprocess, in order to reduce the roughness and to have a predeterminedshape at an edge portion of the wafer that is caused by the slicingprocess, the edge portion of the wafer is polished. In the lappingprocess, in order to improve the flatness on the front and back surfacesof the wafer that have been cut to a given thickness, the surfaces ofthe wafer are polished. In the etching process, in order to removeremaining fine cracks or defects on the surface of the wafer that ispolished in the lapping process, the surface of the wafer is etchedusing a chemical reaction. In the back side polishing process, in orderto improve the flatness of the back side surface of the wafer and toremove damage thereof caused by the etching process, the back sidesurface of the wafer is polished. In the pre-anneal cleaning process, inorder to compensate for an incomplete lattice defect structure occurringon the surface that is caused by the etching process, annealing andcleaning processes are performed on the surface of the wafer. In theedge polishing process, in order to reduce surface damage and poorflatness at the edge portion of the wafer caused by the etching process,the edge portion of the wafer is polished. Finally, in the frontpolishing process, in order to repair damage and improve the flatness ofthe front side of the wafer occurring by the etching process, the frontside of the wafer is polished.

As described above, the wafer manufacturing process produces a polishedwafer by successively performing the ingot growing process, the slicingprocess, the lapping process, the etching process, and the polishingprocesses. More specifically, in the slicing process, an ingot made inthe ingot growing process is cut into thin sheets using a cutting tool.In the cutting tool, a highly tensioned steel wire is wound around aplurality of grooved rollers with a predetermined pitch, and slurry issupplied to the wire. The wire is carried over the grooved rollers alongone direction or in a reciprocative manner at high speed. The ingot ispressed onto the wire at a predetermined speed, while the slurry issupplied to the wire.

Due to the cutting force of the wire, the ingot is sliced into thinsheets of wafer via the slurry.

In the slicing process, the wire and the ingot are formed with acircular section of a predetermined diameter and a feed rate is variedto be high at the beginning and end points of slicing and low at themiddle point, wherein a feed rate refers to a feed speed at which theingot is supplied onto the wire. Accordingly, at the beginning ofslicing, it is difficult for the wire to be positioned at a desiredposition of the ingot. As a result, the sliced wafer may haveundesirably high nanotopography at one or more surface portions thereof,even after successively having achieved the lapping process, the etchingprocess, and the polishing processes. High nanotopography generallycauses a low yield rate of semiconductor chips.

The nanotopography refers to a nanometer scale height variation or anunevenness of a spatial wave produced on a surface of a wafer; roughnessrefers to an A scale height variation, and flatness refers to a μm scaleheight variation in order to indicate fine surface characteristics. Itis desired to develop a design rule capable of preventing poornanotopography in the development of semiconductor technology. A designrule has been developed to improve fine surface characteristics of awafer, that is, a nanometer scale wave depending on a chemical andmechanical composite polishing process referred to as CMP(Chemo-Mechanical Polishing). This process has been adapted to meetobjectives of the slicing process using the wire in the wafermanufacturing process.

In the slicing process, the use of a conventional wire to slice theingot causes poor nanotopography, that is, spatial waves on a surface ofa wafer. When the sliced wafer has high nanotopography, many failedproducts are produced even after successively having achieved thelapping process, the etching process, and the polishing processes.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention, andtherefore, it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

The disclosed embodiments relate to a method and an apparatus forslicing an ingot that may have advantages of improving nanotopography ata surface of a wafer.

An exemplary method and apparatus for slicing an ingot according to anembodiment of the present invention includes firstly slicing one side ofthe ingot with a first wire to form a first slicing portion at thewafer, and secondly slicing the remaining portion of the ingot with asecond wire to form a second slicing portion continued from the firstslicing portion, wherein the first wire has a smaller diameter than thatof the second wire.

The first wire may be an old wire that has previously secondly slicedthe ingot, and the second wire may be a new wire that has not previouslysliced the ingot.

The first wire may be supplied in a range of 1 to 20 kilometers (km) andmay firstly slice one side of the ingot to a depth in a range of 1 to25% of the diameter thereof.

In a further embodiment, a feed speed of the ingot is raised in astepwise manner to the maximum speed (Vmax) or less, the feed speed iscontrolled corresponding to a diameter variance of the ingot, and thefeed speed is maintained to be at the raised speed.

The feed speed may start at a lower speed than a minimum feed speed whencontrolling the feed speed.

In a further embodiment, a first guide beam attached to one side of theingot is sliced by a wire, the ingot is then sliced, and a second guidebeam attached to the other side of the ingot is finally sliced.

Before slicing, the first guide beam may be attached to one side of theingot and a second guide beam may be attached to the other side of theingot by a water-soluble adhesive.

After finally slicing, the sliced first guide beam, the wafer, and thesecond guide beam may be separated.

The sliced first guide beam, the wafer, and the second guide beam may beseparated by water in a range of 70° C. to 95° C.

An apparatus for slicing an ingot according to an exemplary embodimentof the present invention includes first and second work rollers arrangedin parallel to each other, a wire continuously wound around the firstand second work rollers with a predetermined pitch along a longitudinaldirection thereof, an ingot placed onto the wire between the first andsecond work rollers, a slurry supplier for supplying slurry to the wirearranged at one or both sides of the ingot, and a work plate for feedingthe ingot to be sliced onto the wire, wherein the wire is formed with afirst wire and a second wire, the first wire connecting with the secondwire and having a smaller diameter than that of the second wire.

The first wire may be an old wire that has been previously used tosecondly slice the ingot, and the second wire may be a new wire that hasnot been previously used to slice the ingot.

A third work roller may be further provided such that the first, second,and third work rollers are arranged in a triangular layout. Also, twothird work rollers may be further provided such that the first workroller, the second work roller, and the two third work rollers arearranged in a square layout.

An apparatus for slicing an ingot according to an exemplary embodimentof the present invention includes first and second work rollers arrangedin parallel to each other, a wire continuously wound around the firstand second work rollers with a predetermined pitch along a longitudinaldirection thereof, an ingot placed onto the wire between the first andsecond work rollers, a slurry supplier for supplying slurry to the wirearranged at one or both sides of the ingot, and a work plate for feedingthe ingot to be sliced onto the wire, wherein a first guide beam isfurther provided on one side of the ingot by the wire and a second guidebeam is further provided on the other side of the ingot by the workplate.

The first and second guide beams may be respectively formed such thatportions facing the ingot have the same curvature as that of thecorresponding portion of the ingot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus for slicing an ingotaccording to a first exemplary embodiment of the present invention.

FIG. 2 is a top plan view of a sliced wafer according to a firstexemplary embodiment of the present invention.

FIG. 3 is a side view of a sliced wafer according to a first exemplaryembodiment of the present invention.

FIG. 4 is a graph showing a relation of a feed rate of an ingot and aslicing time according to a second exemplary embodiment of the presentinvention.

FIG. 5 is a top plan view of a wafer showing a relation of a feed rateof an ingot with a slicing time of FIG. 4.

FIG. 6 is a perspective view of an apparatus for slicing an ingotaccording to a second exemplary embodiment of the present invention.

FIG. 7 and FIG. 8 are top plan views of a sliced wafer according to athird exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view of an apparatus for slicing an ingotaccording to a first exemplary embodiment of the present invention.

Referring to FIG. 1, an apparatus for slicing an ingot includes first,second, and third work rollers 10, 20, and 30, a wire 40, a slurrysupplier 50, and a work plate 60.

In order to slice the ingot 1 into a plurality of wafers W, the firstand second work rollers 10 and 20 are configured such that a wire 40 isrepeatedly wound over these two rollers 10 and 20 and is supported in atensioned state there between. In detail, the first and second workrollers 10 and 20 are located in parallel, and the first and second workrollers respectively have a plurality of grooves 11 and 21 engravedthereon with a uniform pitch P. To reduce the complexity of FIG.1 only aportion of the grooves 11 and 21 are illustrated. These grooves 11 and21 serve as channels for the wire 40. Also, the grooves 11 and 21 areformed spirally on the outer periphery surface of the first and secondwork rollers 10 and 20. With such structure, the wire can be carriedaround the first and second work rollers 10 and 20 sequentially or in areciprocative manner such that when the wire moves in one directionwhile repeatedly passing around the pair of rollers 10 and 20, it windsits way along the spiral grooves from one end of the rollers 10 and 20to the other end thereof when slicing the ingot 1.

The third work roller 30 is located below the first and the second workrollers 10 and 20 to provide clearance for the wire 40 at the undersideof the rollers 10 and 20 therefrom, so the ingot to be sliced is notinterfered with by the wire 40 beneath the rollers 10 and 20. Two ormore third work rollers 30 may be provided or no third work roller 30may be provided. It is desired that the first, second, and third workrollers 10, 20, and 30 are arranged in a triangular layout (see FIG. 1)or a polygonal layout such as a square layout. When no third work roller30 is provided, the first and second work rollers 10 and 20 may bearranged in parallel. The third work roller 30 has a plurality ofgrooves 31 that may have the same pitch as that of the grooves 11 and 21such that the wire is sequentially carried around the first, second, andthird work rollers 10, 20, and 30. To reduce the complexity of FIG.1only a portion of the grooves 31 are illustrated. As such, the wire 40is sequentially wound around the first, second, and third work rollers10, 20, and 30 according to a triangular layout or another polygonallayout thereof. When no third work roller 30 is provided, the wire 40may be reciprocally wound between first and second work rollers 10 and20.

The wire 40 is formed as a single strand and is sequentially woundaround the first, second, and third work rollers 10, 20, and 30 and isconsecutively wound over the neighboring grooves 11, 21 and 31 of therespective first, second and third work rollers 10, 20 and 30. The wire40 is consecutively wound over the respective first, second, and thirdwork rollers 10, 20, and 30 along the longitudinal direction thereof.The wire 40 forms a layout such that consecutive wire wraps are arrangedin parallel with a uniform pitch P along the respective grooves 11 and21 between the first and second work rollers 10 and 20. The number ofgrooves in the layout determines the number of sheets of wafers W to besliced from the ingot 1. To reduce the complexity of FIG. 1 only aportion of the wafers W are illustrated. When a tensile force F isapplied to one end of the wire 40 along the arrow direction of FIG. 1,the wire 40 is drawn from the other side thereof in a stretched statearound the rollers 10, 20, and 30. The wire 40 is repeatedly wound overthe longitudinal neighboring grooves 11, 21, and 31 of the respectivefirst, second and third work rollers 10, 20, and 30 while the first,second, and third work rollers 10, 20, and 30 rotate in one direction.The first, second, and third work rollers 10, 20, and 30 may be rotatedby means of a friction force from the moving wire or may be rotated by adriving motor (not shown) coupled to at least one of the rollers 10, 20and 30.

The wire 40 may be formed as a highly tensional steel wire such as pianowire. The wire 40 may be formed with a constant diameter. The wire 40may be formed of a first wire 40 a and a second wire 40 b connected toeach other, where the first wire 40 a has a smaller diameter than thesecond wire 40 b. The first wire 40 a may be a used wire which haspreviously been used to slice the ingot 1, while the second wire 40 bmay be a new wire which has not sliced the ingot 1. When beginning theslicing process, the first wire 40 a facilitates a slicing action orfirstly slices one side of the ingot 1, and then the second wire 40 bsecondly slices the firstly sliced side of the ingot 1.

In some embodiments, it is desired that the first wire 40 a be suppliedwith a length in the range of 1 to 20 km. When the first wire 40 a issafely provided at a desired beginning position of the ingot and slicesat the desired position thereof, the sliced wafer W has a thickthickness at the desired portion thereof. The thick portion issubsequently sufficiently polished by successively applying the lappingprocess, the etching process, and the polishing processes, therebyproviding low nanotopography for the wafer. The length of the first wire40 a can be properly determined according to a length of the ingot 1 andthe number of sheets of wafer W to be produced therefrom. In someembodiments, when the ingot 1 has a length in a range of 30 to 45 cm andthe first wire 40 a has a length of less than 1 km, the ingot 1 has ashallow sliced depth thereon. Accordingly, it may be difficult to safelymaintain the wire 40 at the desired position of the ingot 1. Also, insome embodiments when the first wire has a length greater than 20 km,the thick portion may be too deeply formed in the sliced wafer W. Thismay be problematic in that a severe lapping process may then-be needed.

The ingot 1 to be sliced into a plurality of wafers W is placed onto thewire 40. The slurry supplier 50 is provided to the wire 40 such thatslurry is supplied to the wire 40 while slicing the ingot 1. The slurrysupplier 50 may be provided at one side of the ingot 1, and preferablyat both sides thereof. Particularly, when wire 40 is reciprocallymoving, the slurry supplier 50 is provided at both sides of the ingot 1so that the slurry can be efficiently supplied to the wire 40. Thesupplied slurry is attached to the surface of the wire 40 and movesalong with the wire 40.

The work plate 60 is provided for feeding the ingot 1 onto the movingwire 40. The work plate 60 is reciprocally moved while it is secured tothe ingot 1. In other words, the work plate 60 feeds the ingot 1 ontothe wire 40 along the vertical direction of FIG. 1 so that the wire 40can slice the ingot 1 into a plurality of wafers W via the slurry. Themovement of the ingot 1 attached to the work plate 60 is desired to becontrolled at an appropriate feed rate according to a diameter varianceof the ingot 1, a linear speed of the wire 40, and a desirednanotopography of the wafers W.

A wafer for manufacturing a semiconductor is produced by sequentiallyachieving the ingot growing process, the slicing process, the lappingprocess, the etching process, and the polishing processes.

The apparatus for slicing an ingot configured in this manner can slicethe ingot 1 into a plurality of wafers W using different methods.

FIG. 2 is a top plan view of a sliced wafer according to a firstexemplary embodiment of the present invention, and FIG. 3 is a side viewof a sliced wafer according to the first exemplary embodiment of thepresent invention.

Referring to FIG. 2 and FIG. 3, a method for slicing an ingot includes afirst slicing step ST10 and a second slicing step ST20.

In the first slicing step ST10, the first wire 40 a slices one side ofthe ingot 1 to form a first slicing portion W1 at the wafer W. The firstwire 40 a may be an old wire that has been previously used in the secondslicing step ST20, and it may be used by rewinding the same. As notedabove, the length of the first wire 40 a may be provided in the range of1 to 20 km. With such a length, the first wire 40 a can form the firstslicing portion W1 at the wafer W by slicing one side of the ingot 1 toa depth in a range of 1% to 25% of the diameter of the wafer W (e.g.,length L).

The second slicing step ST20 continues from the first slicing step ST10.In the second slicing step ST20, the second wire 40 b slices theremaining portion of the ingot 1 to form a second slicing portion W2that is continuously connected with the first slicing portion W1. Atthis time, the second wire 40 b may be a new wire as noted above.

The first slicing portion W1 has a thickness t1 that is thicker than athickness t2 of the second slicing portion W2, since the first slicingportion W1 has been cut by the smaller diameter first wire 40 a. Inother words, the thickness of a wafer associated with the first slicingportion W1 is ti and the thickness of a wafer associated with the secondslicing portion W2 is t2.

In summary, the first wire 40 a can be safely positioned at one side ofthe ingot 1 as noted above and forms the first slicing portion W1 of athickness t1. Accordingly, the wafer W may have a desired nanotopographyin that the first slicing portion W1 is sufficiently polished in theafter-slicing process such as the lapping, etching, and polishing, etc.

FIG. 4 is a graph showing a relation of a feed rate of an ingot and aslicing time according to a second exemplary embodiment of the presentinvention. FIG. 5 is a top plan view of a wafer showing a relation of afeed rate of an ingot with a slicing time of FIG. 4.

Referring to FIG. 4 and FIG. 5, a method for slicing an ingot accordingto the second exemplary embodiment includes a first slicing step (ST30),a second slicing step (ST40), and a third slicing step (ST50). The curve(a) shows a relation of a feed rate of an ingot to slicing timeaccording to a prior art, and the curve (b) shows a relation of a feedrate of an ingot to a slicing time according to this embodiment of thepresent invention.

In the method for slicing an ingot, a single-diameter wire may be used,or a two-diameter wire may be used with a first wire and a second wirewhere the first wire has a smaller diameter than that of the secondwire, as noted above.

In the first slicing step ST30, a feed speed V of the ingot 1 is raisedin a stepwise manner to the maximum speed Vmax or less. The feed speed Vstarts at a lower speed than a minimum feed speed Vmin of the secondslicing step ST40 and is raised in two steps to a maximum speed Vmax orless. The feed speed V may be raised in two or more steps and the raisedfeed speed V may be the same as the maximum speed Vmax or may be lessthan that.

As such, in the first slicing step ST30, the feed speed V is maintainedto be at a low level and is raised in level in a stepwise manner. As aresult, the wire 40 can be safely positioned onto the ingot 1 at thebeginning of slicing and can slice the same with a stepwise increase inspeed.

Also, the feed speed V is raised in a stepwise manner from a low speedto a high speed so that the wire 40 can be safely positioned onto theingot 1 and a first slicing portion W3 can have the same plane as thatof second and third slicing portions W4 and W5. Accordingly, the wafer Wmay have a desired nanotopography after the first slicing portion W1 issufficiently polished in the after-slicing process such as the lapping,etching, and polishing, etc.

The second slicing step ST40 is continued from the first slicing stepST30. In the second slicing step ST40, the feed speed V is controlled incorrespondence to a diameter variance (c) of the ingot 1. Here, thediameter may relate to the distance across the ingot at the current pathof the wire through the ingot. For example, when the wire 40 moves at aconstant speed and slices one side of the ingot 1 from a smallerdiameter portion to a larger diameter portion, for example, from thepoint 1/8L of FIG. 5 to the center thereof, the feed speed (V) isgradually reduced toward the larger diameter. When the wire 40 passesthrough the center of the ingot 1 and slices the ingot 1 from the largerdiameter portion to the smaller diameter portion, the feed speed (V) isgradually increased toward the smaller diameter portion of the ingot.The third slicing step ST50 is continued from the second slicing stepST40. In the third slicing step ST50, the last portion of the ingot 1 issliced while the feed speed V is maintained to be at, for example, araised speed V.

At this time, the raised feed speed V may be the same as the maximumspeed Vmax or it may be less.

Such a method according to a second exemplary embodiment of the presentinvention may be applied to the apparatus for slicing an ingot (forexample, not including a first guide beam and a second guide beam)according to a first exemplary embodiment of the present invention.

FIG. 6 is a perspective view of an apparatus for slicing an ingotaccording to a second exemplary embodiment of the present invention.

For better understanding and ease of description, features according tothe second embodiment that are the same as in the first embodiment willnot be described in further detail, and only the differences will befocused on in the following description.

An apparatus for slicing an ingot according to a second embodimentfurther includes a first guide beam 70 and a second guide beam 80,compared to the apparatus for slicing an ingot according to the firstembodiment. In the apparatus for slicing an ingot, a singe-diameter wiremay be used or a two-diameter wire may be used with a first wire and asecond wire where the first wire has a smaller diameter than that of thesecond wire as noted above.

The first guide beam 70 is provided on one side of the ingot 1 near thewire 40 and the second guide beam 80 is provided on the other side ofthe ingot 1 near the work plate 60. The first guide beam 70 is firstlysliced, the ingot 1 is sliced, and the second guide beam 80 is finallysliced. It is desirable that the first guide beam 70, the ingot 1, andthe second guide beam 80 are attached with, for example, a water-solubleadhesive, and that the water-soluble adhesive is soluble in water of 70to 95° C. That is, this water-soluble adhesive has a desired adhesivestrength and is removed after being sliced. Accordingly, so that it isnot removed during slicing, the water-soluble adhesive can be removed ata temperature higher than that of the slicing process.

The first guide beam 70 is firstly sliced while the wire 40 ismaintained at a desired position when beginning to slice the ingot 1.Also, the second guide beam 80 maintains the wire 40 at a desiredposition even after slicing the ingot 1 and fixes the sliced wafer sothat it is not directly separated from the remainder of the ingot 1. Asa result, the sliced wafer W can have the desired nanotopography.

Preferably, the first and second guide beams 70 and 80 are respectivelyformed such that portions 71 and 81 (FIG. 8) facing the ingot 1 have thesame or substantially the same curvature as that of correspondingportions 1 a and 1 b (FIG. 8) of the ingot 1. Thus, the first and secondguide beams 70 and 80 can be securely attached to the ingot 1.

FIG. 7 and FIG. 8 are respectively top plan views of a sliced waferaccording to a third exemplary embodiment of the present invention.

A method for slicing an ingot according to the second embodiment of thepresent invention will hereinafter be described in detail with referenceto FIG. 7 and FIG. 8. In this embodiment, a method for controlling thefeed rate may be applied to the method for slicing the ingot. In thiscase, the wafer W can have more improved nanophotography.

The method for slicing an ingot includes a first slicing step ST60, asecond slicing step ST70, and a third slicing step ST80.

In the first slicing step ST60, the wire 40 slices the first guide beam70. When the wire 40 first slices the first guide beam 70 before slicingthe ingot 1, the wire 40 can be positioned at a desired position of theingot 1.

Before the first slicing step ST60, it is preferable that the firstguide beam 70, the ingot 1, and the second guide beam 80 are attachedwith, for example, a water-soluble adhesive.

The second slicing step ST70 is continued from the first slicing stepST60. In the second slicing step ST70, the ingot 1 is sliced. In thiscase, the wire 40 slices a desired position of the ingot 1 while it ismaintained at the desired position by guidance of the first guide beam70.

The third slicing step ST80 is continued from the second slicing stepST70. In the third slicing step (ST80), the second guide beam 80 issliced. Therefore, the wire 40 slices the remaining portion of the ingot1 and continuously the second guide beam 80 while maintaining a desiredposition. The wire 40 slices the last portion of the ingot 1 safely byguidance of the second guide beam 80. After the third slicing step ST80,it is desired that the ingot be removed from the first and second guidebeams 70 and 80, as shown in FIG. 8. The first guide beam 70, the slicedingot, and the second guide beam 80 can be removed from each other in,for example, water at 70° C. to 95° C.

This water-soluble adhesive and water may be appropriately used withoutvarying the nanotopography.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

According to some embodiments of the present invention, the firstsmaller diameter wire firstly slices the ingot 1, and the second largerdiameter wire secondly slices the same.

As a result, the wafer W has a thick thickness at a portion where thefirst wire has sliced. The thick portion can be sufficiently polished bysuccessively applying the lapping process, the etching process, and thepolishing processes, thereby providing a desired nanotopography for thesliced wafer.

Also, this desired nanotopography may have an effect to improve a lowyield rate of semiconductors.

According to some embodiments of the present invention, the feed speedcan be raised in a stepwise manner at a lower speed than the maximumspeed and the ingot can be sliced after the first guide beam has beenfirstly sliced.

As a result, the wire can be safely positioned onto the ingot at thebeginning of slicing so that the sliced wafer has a uniform thickness.

Also, a uniform thickness may have an effect to improve a low yield rateof semiconductors.

1. A method for slicing an ingot into a plurality of wafers via a slurry while the slurry is supplied to a moving wire, the method comprising: slicing the ingot with a first wire to form a first slicing portion for the wafers; and slicing the ingot with a second wire to form a second slicing portion continued from the first slicing portion, wherein the first wire has a diameter that is smaller than a diameter of the second wire.
 2. The method for slicing an ingot of claim 1, wherein the first wire has been previously used to slice the ingot.
 3. The method for slicing an ingot of claim 2, wherein the second wire is a new wire that has not previously sliced the ingot.
 4. The method for slicing an ingot of claim 1, wherein the first wire is supplied in a length in a range of 1 to 20 km.
 5. The method for slicing an ingot of claim 1, wherein the first wire firstly slices one side of the ingot in a range of 1 to 25% of the diameter of the ingot.
 6. A method for slicing an ingot into a plurality of wafers via slurry while the slurry is supplied to a moving wire, the method comprising: raising a feed speed of the ingot in a stepwise manner to a raised speed that is less than or equal to a maximum speed (Vmax); controlling the feed speed in accordance with a diameter variance of the ingot; and maintaining the feed speed at the raised speed.
 7. The method for slicing an ingot of claim 6, wherein the feed speed starts at a lower speed than a minimum feed speed when controlling the feed speed.
 8. A method for slicing an ingot into a plurality of wafers via a slurry while the slurry is supplied to a moving wire, the method comprising: slicing a first guide beam attached to one side of the ingot, with a wire; slicing the ingot; and slicing a second guide beam attached to an other side opposite to the one side of the ingot.
 9. The method for slicing an ingot of claim 8, wherein before slicing, the first guide beam is attached to the one side of the ingot and the second guide beam is attached to the other side opposite to the one side of the ingot with a water-soluble adhesive.
 10. The method for slicing an ingot of claim 8, wherein after slicing the second guide beam, the sliced first guide beam, the wafers, and the second guide beam are separated.
 11. The method for slicing an ingot of claim 10, wherein the first guide beam, the ingot, and the second guide beam are separated with water in a range of 70 to 95° C.
 12. An apparatus for slicing an ingot, comprising: first and second work rollers arranged in parallel to each other; a wire continuously wound around the first and second work rollers with a predetermined pitch along a longitudinal direction thereof; a slurry supplier for supplying slurry to the wire, arranged at one or both sides of the ingot; and a work plate for feeding an ingot to be sliced onto the wire between the first and second work rollers, wherein the wire is formed with a first wire and a second wire, the first wire connected with the second wire, having a smaller diameter than that of the second wire to slice a smaller diameter of the ingot.
 13. The apparatus for slicing an ingot of claim 12, wherein the first wire has previously been used to slice the ingot.
 14. The apparatus for slicing an ingot of claim 13, wherein the first wire has a length in a range of 1 to 20 km.
 15. The apparatus for slicing an ingot of claim 12, comprising a third work roller such that the first, second, and third work rollers are arranged in a triangular layout.
 16. The apparatus for slicing an ingot of claim 15, comprising two third work rollers such that the first, second, and two third work rollers are arranged in a square layout.
 17. An apparatus for slicing an ingot, comprising: first and second work rollers arranged in parallel to each other; a wire continuously wound around the first and second work rollers with a predetermined pitch along a longitudinal direction thereof; a slurry supplier for supplying slurry to the wire arranged at one or both sides of the ingot; and a work plate for feeding an ingot to be sliced onto the wire between the first and second work rollers, wherein a first guide beam is adapted to be provided on one side of the ingot by the wire, and the second guide beam is adapted to be provided on an other side of the ingot by the work plate.
 18. The apparatus for slicing an ingot of claim 16, wherein the first and second guide beams are respectively formed such that portions facing the ingot have the same or substantially the same curvature as that of corresponding portions of the ingot. 